Endovascular prostheses are sometimes used to treat aortic aneurysms. Such treatment includes implanting a stent or stent-graft within the diseased vessel to bypass the anomaly. An aneurysm is a sac formed by the dilation of the wall of the artery. Aneurysms may be congenital, but are usually caused by disease or, occasionally, by trauma. Aortic aneurysms include abdominal aortic aneurysms (“i”), which form between the renal arteries and the iliac arteries, and thoracic aortic aneurysms (“TAAs”), which may occur in one or more of the descending aorta, the ascending aorta, and the aortic arch.